1. Field of the Invention
This invention generally relates to a registration adjusting device for use in an optical writing system, such as a laser beam printer, for adjusting a registration between a scanning light beam and a sheet of recording paper and in particular to a lateral registration adjusting device for adjusting a registration between a scanning light beam and a sheet of recording paper in a lateral direction which is perpendicular to the direction of transportation of the sheet of recording paper.
2. Description of the Prior Art
In a prior art optical scanning writing system, such as a laser beam printer, typically a plurality of paper cassettes storing sheets of recording paper different in size are provided. And, a sheet of recording paper from the selected paper cassette is first transported to a registration roller which is located near the entrance to an image transfer station where an image is transferred to a sheet of recording paper from a rotating photosensitive drum. The sheet of recording paper in transportation is temporarily brought to a halt when its leading edge has come into abutment against the registration roller which is normally kept inoperative and driven to rotate intermittently. In association with the rotation of the photosensitive drum, the registration roller is driven to rotate to thereby cause the sheet of recording paper to advance into the image transfer station.
With such a structure, the registration in the transporting direction, i.e., auxiliary scanning direction, between the image to be transferred from the photosensitive member and a sheet of recording paper to which the image is to be transferred can be obtained at a relatively high accuracy. Thus, the leading edge of the image is located at a desired position on the sheet of recording paper when transferred. However, in the above-described structure, since sheets of recording paper are supplied from different paper cassettes at different locations, there may still be a chance that each sheet of recording paper coming into contact with the registration roller is shifted in the lateral direction (i.e., transverse direction with respect to the paper transportation direction) one from another. If there is such a discrepancy in the lateral direction between the scanning light beam and a sheet of recording paper, there may be a chance that the image transferred is located too close to one lateral edge of the sheet of recording paper or even beyond the lateral edge in an extreme case.
The typical prior art approach is to provide a mechanical alignment mechanism which brings a sheet of recording paper in registration with its lateral direction before the sheet of recording paper comes into abutment against the registration roller. However, such a mechanical lateral registration mechanism suffers from other disadvantages, such as slowdown in processing speed, high cost and difficulty in maintenance.